chore: add CODEOWNERS to auto-request reviews on touched paths (#457)

Closes #417. Starts with @turbomam as owner for all paths; expand as
collaborators take on specific areas. Once populated, branch protection on
main can enable 'require code-owner reviews'.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: turbomam

.github/CODEOWNERS

@@ -0,0 +1,20 @@
+# CODEOWNERS for berkeleybop/metpo
+# Auto-requests review from the owner when a PR touches their area.
+# Start with a single owner; expand as collaborators take on specific areas.
+# See https://docs.github.com/articles/about-code-owners
+
+# Default owner for everything
+*                             @turbomam
+
+# Ontology editing / templates
+/src/ontology/                @turbomam
+/src/templates/               @turbomam
+
+# Python package
+/metpo/                       @turbomam
+
+# Literature mining
+/literature_mining/           @turbomam
+
+# CI / workflows
+/.github/                     @turbomam